Rollup merge of #79036 - cjgillot:steal, r=oli-obk

Move Steal to rustc_data_structures.

compiler/rustc_middle/src/arena.rs

@@ -14,10 +14,10 @@ macro_rules! arena_types {
             [] layouts: rustc_target::abi::Layout,
             // AdtDef are interned and compared by address
             [] adt_def: rustc_middle::ty::AdtDef,
-            [] steal_mir: rustc_middle::ty::steal::Steal<rustc_middle::mir::Body<$tcx>>,
+            [] steal_mir: rustc_data_structures::steal::Steal<rustc_middle::mir::Body<$tcx>>,
             [decode] mir: rustc_middle::mir::Body<$tcx>,
             [] steal_promoted:
-                rustc_middle::ty::steal::Steal<
+                rustc_data_structures::steal::Steal<
                     rustc_index::vec::IndexVec<
                         rustc_middle::mir::Promoted,
                         rustc_middle::mir::Body<$tcx>

compiler/rustc_middle/src/ich/impls_ty.rs

@@ -184,15 +184,6 @@ impl<'a> HashStable<StableHashingContext<'a>> for ty::FloatVid {
     }
 }
 
-impl<'a, T> HashStable<StableHashingContext<'a>> for ty::steal::Steal<T>
-where
-    T: HashStable<StableHashingContext<'a>>,
-{
-    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        self.borrow().hash_stable(hcx, hasher);
-    }
-}
-
 impl<'a> HashStable<StableHashingContext<'a>> for crate::middle::privacy::AccessLevels {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {

compiler/rustc_middle/src/ty/context.rs

@@ -14,7 +14,6 @@ use crate::mir::interpret::{self, Allocation, ConstValue, Scalar};
 use crate::mir::{Body, Field, Local, Place, PlaceElem, ProjectionKind, Promoted};
 use crate::traits;
 use crate::ty::query::{self, TyCtxtAt};
-use crate::ty::steal::Steal;
 use crate::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSubsts};
 use crate::ty::TyKind::*;
 use crate::ty::{
@@ -33,6 +32,7 @@ use rustc_data_structures::sharded::{IntoPointer, ShardedHashMap};
 use rustc_data_structures::stable_hasher::{
     hash_stable_hashmap, HashStable, StableHasher, StableVec,
 };
+use rustc_data_structures::steal::Steal;
 use rustc_data_structures::sync::{self, Lock, Lrc, WorkerLocal};
 use rustc_data_structures::unhash::UnhashMap;
 use rustc_errors::ErrorReported;

compiler/rustc_middle/src/ty/mod.rs

@@ -106,7 +106,6 @@ pub mod outlives;
 pub mod print;
 pub mod query;
 pub mod relate;
-pub mod steal;
 pub mod subst;
 pub mod trait_def;
 pub mod util;

compiler/rustc_middle/src/ty/query/mod.rs

@@ -28,13 +28,13 @@ use crate::traits::query::{
 };
 use crate::traits::specialization_graph;
 use crate::traits::{self, ImplSource};
-use crate::ty::steal::Steal;
 use crate::ty::subst::{GenericArg, SubstsRef};
 use crate::ty::util::AlwaysRequiresDrop;
 use crate::ty::{self, AdtSizedConstraint, CrateInherentImpls, ParamEnvAnd, Ty, TyCtxt};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_data_structures::stable_hasher::StableVec;
+use rustc_data_structures::steal::Steal;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::ErrorReported;

compiler/rustc_middle/src/ty/steal.rs

@@ -1,44 +0,0 @@
-use rustc_data_structures::sync::{MappedReadGuard, ReadGuard, RwLock};
-
-/// The `Steal` struct is intended to used as the value for a query.
-/// Specifically, we sometimes have queries (*cough* MIR *cough*)
-/// where we create a large, complex value that we want to iteratively
-/// update (e.g., optimize). We could clone the value for each
-/// optimization, but that'd be expensive. And yet we don't just want
-/// to mutate it in place, because that would spoil the idea that
-/// queries are these pure functions that produce an immutable value
-/// (since if you did the query twice, you could observe the mutations).
-/// So instead we have the query produce a `&'tcx Steal<mir::Body<'tcx>>`
-/// (to be very specific). Now we can read from this
-/// as much as we want (using `borrow()`), but you can also
-/// `steal()`. Once you steal, any further attempt to read will panic.
-/// Therefore, we know that -- assuming no ICE -- nobody is observing
-/// the fact that the MIR was updated.
-///
-/// Obviously, whenever you have a query that yields a `Steal` value,
-/// you must treat it with caution, and make sure that you know that
-/// -- once the value is stolen -- it will never be read from again.
-//
-// FIXME(#41710): what is the best way to model linear queries?
-pub struct Steal<T> {
-    value: RwLock<Option<T>>,
-}
-
-impl<T> Steal<T> {
-    pub fn new(value: T) -> Self {
-        Steal { value: RwLock::new(Some(value)) }
-    }
-
-    pub fn borrow(&self) -> MappedReadGuard<'_, T> {
-        ReadGuard::map(self.value.borrow(), |opt| match *opt {
-            None => bug!("attempted to read from stolen value"),
-            Some(ref v) => v,
-        })
-    }
-
-    pub fn steal(&self) -> T {
-        let value_ref = &mut *self.value.try_write().expect("stealing value which is locked");
-        let value = value_ref.take();
-        value.expect("attempt to read from stolen value")
-    }
-}